Phase behavior and anomalies of thermodynamic properties in a multi-component near-critical fluid mixture

Phase behavior and temperature dependencies of the pressure and isochoric heat capacity Cρ,x near the liquid-vapor critical point of a hydrocarbon ternary mixture (methane + 0.35 mol fr. of propane + 0.15 mol fr. of pentane) have been studied by high-resolution adiabatic calorimetry. The temperature dependence of the pressure has been investigated for ten different isochores in the density range 0.185-0.444 g/cm3. The heat capacity Cρ,x has been measured for four near-critical isochores. It is shown that in fluid mixtures, in contrast to one-component fluids, an anomaly in the derivative (∂P/∂T)ρ,x emerges along with an anomaly in the isochoric heat capacity Cρ,x. A general approach for the description of physical properties of multi-component mixtures in the vicinity of their critical points based on transformation of scaling fields to experimental field variables is addressed in the theoretical part of the paper. The approach enabled us to describe quantitatively all the data obtained in the experiment. The suggested approach is universal since that it does not depend on the number of the components in fluid mixtures.